Percutaneous vertebroplasty involves the injection of a bone cement or suitable biomaterial into a vertebral body via a percutaneous route under X-ray, ultrasonic, magnetic resonance imaging, or other visual guidance. The cement is injected as a semi-liquid substance through a needle that has been inserted into the vertebral body, generally along a transpedicular or posterolateral approach. The three main indications for vertebroplasty are benign osteoporotic fractures, malignant metastatic disease and benign tumors of the bone. Traumatic fractures of weakened bone or traumatic fractures of normal bone can also be treated by the methods described here. The bone cement materials injected into a vertebral body may be derivatives of polymethyl methacrylate (PMMA) or biologically active substances such as calcium triphosphate, calcium phosphate or hydroxyapetite or bone morphogenic protein (BMP).
Percutaneous vertebroplasty provides structural reinforcement of a vertebral body through injection, by a minimally invasive percutaneous approach, of bone cement material into the vertebral body. See, for example, Vasconcelos, C. et al., Is percutaneous vertebroplasty without pretreatment venography safe? Evaluation of 205 consecutive procedures. Am. J. Neuroradiol. 2002, June-July; 23(6): 913-7. Percutaneous vertebroplasty can result in increased structural integrity, decreased micromotion at the fracture site, and possibly a destruction of pain fibers due to the heat of the bone cement as it polymerizes and sets. Complete pain relief can be achieved in up to eighty percent of patients. The cement material should have properties that, when injected, can increase vertebral body stiffness and compressive strength. Any cement materials having these properties that are commonly known or become known to one of skill in the art may be used. The cement should be fluid enough to flow into fracture planes and to fuse them. Although there is some debate about the appropriate thermal properties, it is believed by some that the heating effect can be beneficial and cause death to local nerve endings involved in pain stimulation. It is generally accepted that most pain relief is achieved due to increased structural integrity.
When performing vertebroplasty, a needle of an appropriate gauge (for example, an eleven gauge or thirteen gauge in a smaller vertebral body) is passed down the pedicle until it enters the vertebral body and reaches the junction of the anterior and middle thirds. The needle is inserted at a suitable angle and passed through the periosteum, down the pedicle and into the vertebral body. Insertion of the needle may require a large applied force. For example, a large force may be required when entering the cortex and in the transition from the pedicle to the vertebral body.
A suitable cement material is prepared, injected through the needle and into the vertebral body, under lateral X-ray projection fluoroscopy imaging. Injection of the cement continues until adequate vertebral filling is achieved. The injection is discontinued if the cement starts to extend into some unwanted location such as the disc space or towards the posterior quarter of the vertebral body, where the risk of epidural venous filling and hence spinal cord compression is greatest.
Exemplary needles for use in vertebroplasty are disclosed in U.S. Pat. No. 6,749,595, which is incorporated herein by reference. Typically, an injector system or a syringe may be attached to the needle for pressurized delivery of the cement to the vertebral body. Due to the high pressure used to inject the cement into the vertebral body, complications of vertebroplasty include a risk of extravasation of cement into the venous system and further embolization to the lungs. These complications can cause cord compression and paralysis or pulmonary embolism and death. Murphy et al., A Review of Complications Associated with Vertebroplasty and Kyphoplasty as Reported to the Food and Drug Administration Medical Device Related Web Site, Journal of Vascular and Interventional Radiology, in press.
Thus, a need exists for a cement delivery apparatus that can withstand the rigors of insertion into a patient undergoing percutaneous vertebroplasty and that allows for delivery cement in a controlled manner to avoid complications associated with high pressure delivery of the cement to the vertebral body.